1. Field of the Invention
The present invention relates to a pressure sensor, and in particular, to one suitable for automotive use or the like.
2. Description of the Related Art
FIG. 11 is a block diagram illustrating an example of the construction of a known semiconductor pressure sensor. An element portion 1 for detecting pressure is, for example, formed on a diaphragm D which is adapted to be deformed by an external force to be measured and acting thereon as shown in FIG. 12, and the element portion 1 is comprised of a bridge circuit including semiconductor gauge resistors RA-RD (a resistor RD is arranged at a side opposite a resistor RA) whose resistances change due to distortions thereof caused by the deformation of the diaphragm D. Note that a symbol R1 designates a temperature characteristic compensation resistor, and a symbol T designates a constant current circuit.
In FIG. 11, the known pressure sensor includes the element portion 1 for detecting the above-mentioned pressure, and a circuit portion 2 having a signal processing function. The circuit portion 2 includes a first integrated circuit (IC) 3 and a second integrated circuit (IC) 4 for storing bit data 22 to adjust and compensate for the initial variation and temperature dependency of a bridge circuit output 41 of the element portion 1. The second IC 4 includes an analog processing section 21 which operates to receive the bridge circuit output 41 of the element portion 1 and generates an analog output corresponding to the pressure applied to the diaphragm D, a characteristic adjustment and compensation section 23 for adjusting and compensating for the initial variation and temperature dependency of the bridge circuit output 41 of the element portion 1 based on the above-mentioned bit data 22, and an interface section 24 optimized to interface with external wiring.
Now, the operation of the known pressure sensor as illustrated in FIG. 11 will be described below in detail. When the diaphragm D (see FIG. 12) arranged at the element portion 1 receives an external force to be measured and is deformed thereby, the resistances of the semiconductor gauge resistors RA-RD, which are formed on the diaphragm D and whose resistances change in accordance with the distortion of the diaphragm D, change, thus resulting in a change in the output 41 of the bridge circuit comprised of the semiconductor gauge resistors RA-RD illustrated in FIG. 13. This change is amplified by the analog processing section 21 incorporated in the second IC 4 to provide a desired output SPAN.
The bridge circuit output 41 from the element portion 1 changing in accordance with the pressure applied to the diaphragm D usually varies depending upon individual elements. This is due to differences in the element detection sensitivities of the individual elements. At this time, in order to easily obtain the desired output SPAN for different element detection sensitivities varying in accordance with the individual elements, there is employed a technique or the like for controlling the amount of current supplied to the bridge circuit, as disclosed in Japanese Patent Application Laid-Open No. 9-218118 for instance.
According to this current amount controlling technique, the magnitude of the voltage to be supplied to resistors, which determine the amount of current flowing in the constant current circuit, is changed by giving the voltage in terms of bit data 22 stored in the first IC 3. The bit data is given via a communications channel 42 to the characteristic adjustment and compensation section 23, which is incorporated in the second IC 4 for adjusting and compensating for the initial variation and temperature dependency of the bridge circuit output 41 of the element portion 1.
With the above arrangement, it is possible to compensate for the element detection sensitivities, which change depending on the temperature for instance, by changing the bit data to be used depending on the temperature. The signal thus obtained according to the above operation is output as an analog signal 32 through the interface section 24 optimized to interface with external wiring.
The environments around motor vehicles in recent years have been greatly changed, and hence, system environments such as a surrounding environment of securing the tolerance to electromagnetic waves of very high frequencies, an environment in which sensor signals can be commonly used for various kinds of systems, in particular such a system environment in which sensor signals can be freely read in at timing as required by systems, have come to be demanded even in the field of motor vehicles.
A method of materializing this is a vehicle mounted LAN, and for instance there is a CAN or the like as such a method. This CAN method handles voltage information, which has usually been handled as an analog signal, by digitizing and converting it into a serial signal represented by bits. This has a merit in that there can be easily realized such a system environment in which the tolerance to noise such as electromagnetic waves can be greatly improved, and in which a sensor signal can be freely read in at timing as required by the above-mentioned system.
On the other hand, inexpensive sensors having a minimum function come to be demanded even more than before, and hence there is a problem with these contradictory demands in that the known pressure sensor configuration as illustrated in FIG. 11 is particularly difficult to adapt to the CAN method. In order to adapt the known sensor to the CAN system, it is at least necessary to add a CAN driver for interfacing with a bus line, a digital processing section for arithmetically processing and controlling a serial signal output in conformance with the CAN requirements, and an encoding section for digitally encoding an analog signal of the sensor. However, there arises another problem that the number of component members to be added for this purpose is not desirable or suitable for achieving miniaturization and cost reduction of the sensor for automotive use.
The present invention is intended to obviate the problems as referred to above, and has for its object to provide a pressure sensor which has greatly improved tolerance to noise such as electromagnetic waves, is configured such that a system environment is able to be easily selected in which a sensor signal can be freely read in at timing as required by the above-mentioned system, and is able to realize reduction in the size and cost thereof suitable for automotive use.
Bearing the above object in mind, according to one aspect of the present invention, there is provided a pressure sensor including an element portion for detecting pressure and a circuit portion having a signal processing function, both of which are integrally accommodated in the same package. The circuit portion comprises: a first section for performing analog processing of a detection signal from the element portion; a second section for storing bit data for characteristic adjustment and compensation and performing characteristic adjustment and compensation of the detection signal from the element portion based on the bit data; an interface section optimized to interface with external wiring; an A/D conversion section for digitally encoding the analog processed detection signal; and a digital processing section for converting the digitized signal into a desired serial signal.
Preferably, the pressure sensor includes an analog signal output and a digital signal output which are selectable between two output forms inclusive of an analog processed detection signal and a digital processed detection signal.
Preferably, the A/D conversion section and the digital processing section are incorporated in a first IC, whereas the interface section is incorporated in a second IC different from the first IC.
Preferably, the first IC comprises a section for storing the bit data, an A/D conversion section for digitally encoding the analog processed detection signal, and a digital processing section for converting the digitized signal into a desired serial signal, and the second IC comprises a section for performing analog processing of the detection signal from the element portion, a section for performing characteristic adjustment and compensation based on the bit data, and a serial interface section suitable for generating a serial output to the external wiring.
Preferably, the first IC comprises a section for storing the bit data, an A/D conversion section for digitally encoding the analog processed detection signal, a digital processing section for converting the digitized signal into a desired serial signal, a section for analog processing the detection signal from the element portion, and a section for performing characteristic adjustment and compensation based on the bit data, and the second IC comprises a serial interface section suitable for generating a serial output to the external wiring.
Preferably, the first IC comprises a section for performing analog processing of the detection signal from the element portion, a section for storing the bit data and performing characteristic adjustment and compensation based on the bit data, an A/D conversion section for digitally encoding the analog processed detection signal, and a digital processing section for converting the digitized signal into a desired serial signal, and the second IC comprises an interface section optimized to interface with the external wiring, and the first and second ICs are each provided with two output ports for the analog processed detection signal and the digital processed detection signal.
Preferably, the first IC comprises a section for performing analog processing of the detection signal from the element portion, a section for storing the bit data and performing characteristic adjustment and compensation based on the bit data, an A/D conversion section for digitally encoding the analog processed detection signal, and a digital processing section for converting the digitized signal into a desired serial signal, and the second IC comprises an interface section optimized to interface with the external wiring, and the first IC is provided with two output ports for the analog processed detection signal and the digital processed detection signal, and uses the output port for an analog signal, and the second IC is provided with the interface section for an analog signal suitable for an analog output.
Preferably, the first IC comprises a section for performing analog processing of the detection signal from the element portion, a section for storing the bit data and performing characteristic adjustment and compensation based on the bit data, an A/D conversion section for digitally encoding the analog processed detection signal, and a digital processing section for converting the digitized signal into a desired serial signal, and the second IC comprises an interface section optimized to interface with the external wiring, and the first IC is provided with an analog signal output port and a serial signal output port for the analog processed detection signal and the digital processed detection signal, respectively, and uses the serial signal output port, and the second IC is provided with the interface section for a serial signal suitable for a serial output.
Preferably, the pressure sensor further comprises a single conductor line connecting between the first and second ICs for communications of the analog processed detection signal or the digital processed detection signal therebetween.
Preferably, the pressure sensor further comprises a power supply input port for receiving electric power from an external power supply, and a power supply circuit for generating a voltage which has a ratio metric relation with respect to an input voltage supplied to the power supply input port and which has dropped from the input voltage from the external power supply, and the respective sections other than the power supply circuit and the interface section are configured to be operated by the dropped power supply circuit output.
Preferably, the first IC provided with the interface section comprises a power supply input port for receiving electric power from an external power supply, a power supply circuit for generating a voltage which has a ratio metric relation with respect to an input voltage supplied to the power supply input port and which has dropped from the input voltage from the external power supply, and a power supply output port for supplying the dropped power supply circuit output to the second IC, and the respective sections other than the power supply Circuit and the interface section are configured to be operated by the dropped power supply circuit output.
According to another aspect of the present invention, a pressure sensor has an element portion for sensing pressure and a circuit portion with a signal processing function integrally accommodated in the same package. Added to the circuit portion are an interface section optimized to interface with external wiring, an A/D conversion section for digitally encoding an analog processed detection signal of the sensor, and a digital processing section for converting the digitized signal into a desired serial signal. The entire circuit portion is constituted only by at most two ICs, and a selection can be made between two output forms including the analog processed detection signal and the digital processed detection signal.
With this arrangement, the tolerance to noise such as electromagnetic waves can be greatly improved, and at the same time, it can be configured such that a system environment is able to be easily selected in which a sensor signal can be freely read in at timing as required by the above-mentioned system. Additionally, it becomes possible to easily achieve the miniaturization and cost reduction of the sensor suitable for automotive use.